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Varanus indicus Print E-mail
Mangrove monitor

Extract from A Little Book of Monitor Lizards © D. Bennett 1995. Viper Press, UK

Varanus indicus indicus       Daudin  1802  Mangrove monitor
Varanus indicus kalabeck      Lesson  1802  Kalabeck monitor
Varanus indicus spinulosus    Mertens  1941 George's Island monitor

The mangrove monitor is a large active lizard with an enormous distribution. Its scientific name is misleading because the species does not occur in India, or anywhere near it. Mangrove monitors are found from northern Australia and New Guinea east to the Solomon Islands, Marshall Islands, Caroline Islands and Marianas Islands. Its distribution through much of Micronesia remains uncertain. Luxmoore et al (1988) give the following locations: Micronesia (Kosrae, Mortlock, Woleai, Ifalak, Yap, Ulithi and several islands in the Truk Atoll), Guam, Indonesia (eastern sector: Irian Jaya and adjacent islands, north to the Talaud Group and west to Halmahera and the Moluccas (Ambon, Buru, Ceram etc.) and Timor, Marshall Islands, Palau (Ngeaur, Oreor, Babeldaob (Babelthaup) Ncheangel (Kayangel) and Solomon Islands (Guadalcanal, Isabel, Malaita and San Christobal). In Australia they are found only in the extreme north; Arnhemland and especially Cape York, Queensland. Reports of V.indicus in Sulawesi appear to be incorrect (Indraganeali, pers. comm.) but they may exist on Obi or Halmahera in broad sympatry with V.salvator. Additional location data can be found in Peters & Doria (1878), Hediger (1934), McCoy (1980); Heatwole (1975), Fisher (1948), Brandenberg (1983); Mertens (1958) and Burt & Burt (1932). Within this massive range there is a huge amount of variation in size, pattern and scalation and major revision of the group is underway. A previously unknown species from New Britain, V.doreanus, has been recently rediscovered (Bohme, Horn & Zeigler 1994). The V.indicus group represent a taxonomist's paradise, providing he or she does not get sea-sick.

V.indicus kalabeck (from the Waigeu Islands off New Guinea) has small widely spaced scales on the neck and was not considered a valid subspecies by Brandenberg (1983). Bohme (1991) notes that the type specimen of V.i.kalabeck is lost and supports Brandenberg's view that the animals on Waigeu are typical mangrove monitors. Live "Kalabeck's monitor" are advertised by animal dealers in North America, but as far as I can ascertain these animals are actually V.doreanus.

V.indicus spinulosus has a shorter, bulkier snout than the typical mangrove monitor and is further distinguished by its spiny scales on the back and neck and nostrils which are situated closer to the tip of the snout than in the nominate race. They are dark in colour, with large dirty-yellow spots over the back. Only one specimen, collected in 1897 on George's Island in the Solomons, was known to science until live specimens were imported to the U.S.A. in the 1980s. These animals are said to come from forests on the larger neighbouring Ysabel Island, where typical mangrove monitors are also found. On this basis Sprackland (1993, 1994) considers it a separate species.

The mangrove monitor attains different sizes in different parts of its range. Swanson's (1976) claim that they reach 200cm TL is probably an overestimate. Schmida (1985) claims they reach 150cm TL and Cogger (1981) gives a total length of 100cm for Australian specimens. In the Solomon islands they average 50cm SVL (125cm TL). The largest from New Britain examined by Hediger (1934) was 124cm TL. On islands and cays of eastern New Guinea they reach 100cm TL whilst on Ceram they reach almost 140cm TL (Edgar, pers. comm.). The largest from Lego, northern Papua, was 34cm SVL (Room 1974). The largest found on Guam by Wikramanayake & Dryden (1988) were 58cm (male) and 44cm (female) SVL with weights of 1900g and 500g respectively. Whether such great size differences between the sexes exist throughout the range is not yet certain, but seems likely.

Mangrove monitors are always found close to water. In northern Australia they are restricted to mangroves (Cogger 1981) and in New Guinea they are never found far from the coast. In the Yap group they were found in forests and swamps (Fisher 1948). In the Solomons they are said to prefer more open areas to thick forest and to be common in coconut plantations (McCoy 1980). In mangrove swamps they prey largely on crabs (Dryden 1965, Uchida 1967, McCoy 1980). They  also take small mammals, snails, birds and their eggs, other lizards, the eggs and young of turtles and crocodiles, slugs, worms and a variety of insects (Tanner 1951; Swanson 1976; Webb et al 1977, Dryden & Taylor 1969, Losos & Greene 1988). In captivity they prey avidly on fish and these are probably taken in the wild where conditions permit. Traeholt (1993) noted that water monitors appeared unable to catch fish in deep water, but mangrove monitors appear to have no such problems and in captivity have been known to polish off large (and expensive) shoals of rainbowfish in just a few hours (Behler, pers.comm.). The fact that prey animals are taken from underwater, on and below the ground and from trees testifies to  the ubiquitous behaviour of this monitor lizard. They swim and dive as well as any other goanna, can climb with great agility, leap from high trees or rocks and can dig proficiently (Hediger 1943, Bustard 1970). In some areas they spend most of their time in the water, either resting or looking for food, whilst elsewhere they are more terrestrial in habit. Similarly in many areas they will take refuge in water when alarmed, but in the Solomons, for example, they are more likely to take shelter in a tree. Studies in Guam have shown that at least during the warmer parts of the year activity occurs only in the mornings (Dryden 1965). Here most breeding probably occurs early in the dry season (Wikramanayake & Dryden 1988). In captivity specimens from Guam have laid eggs in most months of the year (Groves pers.comm.) and Brandenberg (1983) examined recently hatched animals collected in almost every month of the year from New Guinea. Mating and combat, performed quadrupedally, are described by McCoid & Hensley (1991).



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